In the production and fitting of solar panels to roofs of buildings, tracker structures or fixed ground mounting structures, transport and final installation costs are significant. By the nature of their characteristics, solar panels consist of thin laminates, the rigidity of which is critical to their performance and durability under various weather conditions in different geographical regions of the world.
Some PV solar panels known today are planar laminated products. They consist of a front glass “superstrate”, a multiplicity of solar cells encapsulated by a polymer and a back sheet. These are bonded into one planar panel by a lamination process. Some laminates are supported by an aluminum frame. For installation of such a PV panel, this frame may be mounted on an underlying support structure by four mounting devices. The mounting devices may be screwed clamps. This requires assembly of a number of small parts at the installation site, which is a time-consuming method of fixation. When the panels are correctly mounted in accordance with the installation manual for solar panels, they are able to withstand mechanical loads which can be induced by snow and wind.
Some types of panels are frameless. These are typically attached by aluminium clamps lined with rubber. This configuration generally gives a lower load-bearing capacity, particularly if the glass is thin. Another configuration is glass-glass laminates with adequate stiffness, but with the disadvantage of a higher weight. The present invention relates to PV panels for grid connection. PV panels for grid connection normally require certification by independent authorities e.g. TUV Rheinland or Underwriters Laboratory (UL).
The solar cells are generally vulnerable to stress, which may lead to micro-cracks and accompanying power loss. It is therefore desirable to have an essentially stiff panel when installed. The planar stiffness of the panel may be achieved by the glass superstrate and the frame, sometimes with additional reinforcement rails across the back sheet. The moment of inertia increases with glass thickness and height of frame members, thereby providing increased rigidity. However, the penalty with thicker glass is increased weight, reduced heat transfer properties, and more difficult handling and installation work. If the height of the frame is increased, the penalty is greater packaging volume and associated transport costs.
Heretofore it has been known to have strengthening stiffener components added to a solar panel at the point of manufacture. For instance CA1,111,535A1, (Exxon-1981) presents a support structure on the rear-side of the solar cell panel which is formed of a lightweight high strength plastic material having integral rib stiffeners to provide longitudinal and lateral stiffness. These rib stiffeners can be formed by plastic molding and permanently joined directly onto the back of the solar panel during the manufacturing phase. Hence the system in CA1,111,535A1 is dependent solely on a plastic structure for supporting the panel under load. Plastic is a relatively soft material and therefore CA1,111,535A1 discloses a large structure which is relative thick, resulting in low packaging density.
DE4,014,200A1, (Telefunken-1990) describes a frameless solar panel with a glass covered front-side and mounting profiles on the rear-side with an elastic joining material. The mounting profiles are glued to the rear-side of the laminate at the initial manufacturing stage to form permanent stiffening, and can have different shapes such as “U”, “L” or “T” profiles. With this solution the joining material will potentially suffer from fatigue due to thermally induced movement between parts with different thermal expansion coefficients.
DE102005,057,468A1, (Solarwatt-2007) describes a large frameless panel with high stability and stiffness obtained from a box or frame structure on the rear-side. The box or frame structure is permanently fixed to the panel at the point of manufacture. Again, with this solution the joining material can potentially suffer from fatigue due to thermal cycling since the adhesive joins materials of different thermal expansion coefficients.
WO2009/158,715A2, (Sunpower-2009) describes a solar panel with a plastic frame which has permanent strengthening shapes formed on its reverse face at the point of manufacture. This specification also discloses interconnecting capabilities which enable the panel to be laid out directly on a flat (e.g. roof) surface. More than one such panel can be interconnected without the need of additional mounting structures. When the permanent stiffening shapes are formed with or connected to the panel at the time of manufacture, the product suffers from the disadvantage of being of a substantial volume to transport to site.
In all four examples of prior art described above, the specifications deal with permanent stiffening which is integrally formed or added at the point of manufacture, and so leads to an increased total volume which it is necessary to transport with the panel to the point of use (as compared with the actual volume of the solar panel).
WO2009/102,772A2, (Applied Materials-2009) describes a large frameless panel which has stiffening profiles glued on to the rear-side at the time of installation for obtaining stiffness when installed. The gluing process is described to be performed “on site” which is critical with respect to quality. Hence the method of cleaning and drying the panel prior to the gluing process and the related tooling are significant parts of the disclosure. The use of adhesive bonding requires closely controlled surface preparation, aging time and a subsequent curing process at elevated temperature and humidity levels. Such bonding is an expensive operation to perform on site. It is difficult to achieve high quality adhesive bonding on site in variable weather conditions.
There is therefore a need to provide improved PV generator panels, the panels having the required stiffness when installed to ensure long term operational performance in challenging environments, together with compact geometries to reduce material use and aid transportation, thereby providing the potential for cost reduction and significantly reduced environmental impact.